1. Field of the Invention
The present invention relates to gloss control when an image is formed on a print medium.
2. Description of the Related Art
Inkjet printing apparatuses are classified into a serial-type inkjet printing apparatus in which a printhead scans the printing area in vertical and horizontal directions and a line-head type inkjet printing apparatus where nozzles extend on the full width of the printing area, and scanning is performed in only one direction. The serial-type inkjet printing apparatus, which is low cost, is being widely used. With the serial-type inkjet printing apparatus, images are sequentially formed on a print medium by, while ink is ejected from the printhead, alternately repeating printing main-scanning in which a carriage including a printhead is moved/scanned on the print medium and sub-scanning in which the print medium is conveyed by a predetermined amount in a direction perpendicular to the direction in which printing main-scanning is performed. The serial-type inkjet printing apparatus generally employs a printing method called multi-pass printing in which an image is formed in stages by performing a plurality of printing scans on the same image area of the print medium.
Also, demand for improved weather resistance and water resistance of printed matter is increasing in recent years, and pigment ink containing, as a color material, a pigment having superior weather resistance and water resistance is being developed. Unlike dyes that are present in the form of molecules, pigment ink is present in solvents in the form of particles having a size of several ten nanometers to several micrometers. It is generally known that in pigment ink, the size of color material is larger than that of dye ink, and it is therefore possible to obtain printed matter having a high weather resistance. In addition, the pigment particles are not soluble in water, and thus pigment ink is superior to dye ink in terms of water resistance as well.
However, when printing is performed using pigment ink, the pigment particles hardly permeate into the print medium and thus accumulate on the print medium surface. Accordingly, a phenomenon occurs in which the fine regularity (smoothness) of the image surface differs between a printed area and a non-printed area. Also, the amount of color material used differs depending on the density and color of the print image to be reproduced on the print medium, and therefore the amount of area covered by the color material in the print medium differs. Because the reflectivity of the color material and that of the print medium are different, as a result, the difference in the amount of area covered by the color material in the print medium will be recognized by the user as a difference in gloss. In other words, when printing is performed using pigment ink, the gloss level will differ depending on the density and color of the print image to be reproduced. Consequently, so-called “gloss non-uniformity” will occur in which areas having different gloss levels are formed in the same print image. Particularly when non-uniform gloss occurs in photographic printed matter, it is often recognized as an image flaw.
To address this, Japanese Patent Laid-Open No. 2005-297212 (Patent Document 1) discloses a technique in which the number of passes and the mask pattern for multi-pass printing are changed according to the gloss level of the print medium. Specifically, this technique performs multi-pass printing by changing the number of passes, the mask pattern and the concentration of pixels, in order to control the smoothness of the print medium surface depending on accumulation of the pigment ink.
It was found, however, when the technique of Patent Document 1 is applied to multi-pass printing in which the amount of ink per pass is small, it may not be possible to sufficiently control the smoothness of the print medium surface depending on accumulation of the pigment ink.
According to the present invention, even in multi-pass printing, the smoothness of the print medium surface depending on accumulation of the pigment ink is suitably controlled.